In many sports, athletes cover great distances. In order to reduce the required energy, the weight of sports shoes may be reduced. A reduced weight requires less force during accelerations, for example, and thus reduces the strain on the muscles of an athlete.
An essential factor determining the weight of a shoe is the material of the shoe upper. The weight of the shoe upper may in theory be reduced by simply using less material, for example, by reducing material thicknesses. On the other hand, the shoe upper has to fulfill high quality standards, for example with respect to abrasion resistance, flexibility, lamination, resistance, or stability. In order to fulfill such requirements, multilayer or composite materials may be desirable.
Different shoe uppers with multilayer materials are known in the prior art, such as the combination of a textile material with a plastic layer. For example, DE 10 2009 028 627 A1 describes a shoe upper with textile materials, for example a nylon fabric. The textile material may be additionally enhanced on the outside and/or the inside by an appropriate coating, for example by a transparent layer made from thermoplastic polyurethane (“TPU”), which is glued onto the textile material with hot glue.
US 2010/0037483 A1 describes a material for a shoe upper in which fibers are arranged between a base layer and a cover layer for which a thermoplastic polymer material, for example TPU, may be used. Similar materials for a composite material for a shoe upper are described in U.S. Pat. No. 3,397,418, U.S. Pat. No. 6,558,784 B1, and U.S. Pat. No. 7,941,942 B2. Furthermore, US 2007/0199210 A1 describes a material in which a middle layer is arranged between a first layer and a second layer. The middle layer is a textile fabric, and the first and the second layers are made from a foam material, for example, ethylene-vinyl acetate (“EVA”) foam.
US 2011/0088282 A1 describes a composite material for a shoe upper having an outer skin layer and a substrate layer, between which a fabric layer is arranged. The substrate layer may comprise a laminate with a first material layer (for example leather) and a second material layer (for example TPU). The outer skin layer may comprise TPU or a multilayer material, for example an outer layer from thermoset polyurethane (“PUR”) or TPU and an inner layer from TPU.
Another point to be considered, in particular for a shoe upper for a sports shoe, is the stability and response of the upper to different forces. During sporting activities, comparatively large forces may be exerted onto the shoe upper, e.g. during running or when kicking a soccer ball. Furthermore, such forces typically act in a multitude of different directions, depending on the specific movements of the wearer/athlete typically performed during such activities.
In order to provide sufficient stability to the athlete, in particular the foot, and to prevent injuries, the shoe upper has to withstand these forces and protect the foot from external influences. The upper must not tear or lose its shape under the acting stress that is caused by the wearer's movements.
Materials known from the prior art often have certain directions in which their tensile strength is particularly high. Under stress forces acting at an angle to these preferred directions, however, these materials typically deform, shear, or even tear to some degree, which may have a negative effect on the wearing properties of a shoe with an upper made from such a material.
Moreover, in general, the requirements of low weight and stability compete with each other. Trying to minimize the weight of the material typically means losing some stability and tensile strength of the material, at least in some directions, while a high degree of stability and tensile strength typically necessitates the use of thicker or denser materials and therefore leads to an increase in weight.
It is therefore an object of the present invention to provide a material for a shoe upper that at least partly overcomes these disadvantages and combines improved stability with a low weight.